“Drug release” refers to the process in which drug solutes migrate from its position within the release modifying compound or compounds into the medium. Drug release is an important topic in the field of drug delivery for decades. With advancement in material design and engineering, novel materials with increasing complexity and more functions have been introduced into the development of drug delivery devices and systems.
In general, development of an effective drug delivery system requires understanding of the chemical and physical properties that affect i) the interaction between the drug and the micro-nano-particles (carriers), and ii) the interaction between the micro-nano-carries and the biological environment. Often, the structural characterization of the interaction between drug and carrier is missing. Dopant molecules can be either located between individual crystallites of polycrystalline materials or entrapped inside single crystals where they can mimic the stereochemical features of the host.
Molecules, macromolecules and polymers are vastly used to control drug release. Controlling drug release has direct impact on the bioefficacy, the clinical effect and often times on the quality of life of the target patient population.
There are various factors that influence drug release such as: solute diffusion, polymeric matrix swelling, and material degradation. Fick's law of diffusion provides the fundament for the description of solute transport from polymeric matrices. Fickian diffusion refers to the solute transport process in which the polymer relaxation time (tr) is much greater than the characteristic solvent diffusion time (td). When tr≈td, the macroscopic drug release becomes anomalous or non-Fickian.
Nano- and micro-particles hold great promise for controlled and targeted drug release and delivery. An ideal drug carrier should not exert harmful effects on normal cells. It should also satisfy requirements of stability, in vivo biocompatibility, and ability of targeted on-demand release. Inorganic nanomaterials may fulfill most of these requirements. Due to the simplicity of synthesis and modification, it is possible to control the particle size, shape and surface functionalization. Inorganic nanomaterials are usually made of durable and robust materials, which allow encapsulation and protection of sufficient amounts of cargos, preventing pre-leakage and damage to normal cells.
The purpose of mathematical modeling is to simplify the complex release process and to gain insight into the release mechanisms of a specific material system. However, the existing mathematical models may be insufficient in describing more complex material systems, e.g. delivery systems integrating multiple material components, or stimuli-triggered delivery systems in which the interaction with complex physiological condition is involved.